Hadith Qudsi 1

On the authority of Abu Hurayrah (may Allah be pleased with him), who said that the Messenger of Allah (PBUH) said: When Allah decreed the Creation He pledged Himself by writing in His book which is laid down with Him: My mercy prevails over my wrath.

It was related by Muslim (also by al-Bukhari, an-Nasa'i and Ibn Majah).